Method for eliminating electrical arcing during photoelectrophoretic imaging

ABSTRACT

Method and apparatus for eliminating corona arcing during imaging of an electrophoretic imaging system having an elongated blocking electrode and an injecting electrode contacting each other during imaging to form a contact zone and applying a field confined within the area of the contact zone.

llnite Stats met [19] Severynse METHOD FOR ELIMINATHNG ELECTRICAL ARCllNG DURING PHOTOIELECTROPHORETIC IMAGING [75] Inventor: Gerard T. Severynse, Fairport, NY. [73] Assignee: Xerox Corporation, Rochester, NY. [22] Filed: Apr. 13, 1972 I [21] App]. No.: 243,880

Related US. Application Data [62] Division of Serr No. 821,255, May 2, 1969, Pat. No.

[52] US. Cl. 96/1.3, 9 6/1 PE, 204/181 PE [51] lint. Cl. 603g 13/00, G03g 17/00 [58] Field of Search 96/1 PE, 1.3; 204/181 PE [56] References Cited UNITED STATES PATENTS 3,427,242 2/1969 Mikajlov 96/1 PE Dec. 110, 11974 3,448,025 6/1969 Krieger et al1 96/1 PE 3,474,019 10/1969 Krieger et al. 96/1 PE 3,551,313 12/1970 Walsh l 96/1 PE 3,657,091 4/1972 Forest 96/1 PE Primary Examiner-David Klein Assistant Examiner lohn R. Miller Attorney, Agent,'0r Firm-James .l. Ralabate; David C. Petre; Charles E. Smith [5 7] ABSTRACT Method and apparatus for eliminating corona arcing during imaging of an electrophor'etic imaging system having an elongated blocking electrode and an injecting electrode contacting each other during imaging to form a contact zone and applying a field confined within the area of the contact zone.

2 Claims, 3 Drawing Figures CROSS REFERENCE TO RELATED APPLICATION This is a division of application Ser. No. 821,255, filed May 2, 1969, now U.S. Pat. No. 3,697,408 issued Oct. 10, 1972.

This invention relates in general to imaging systems and more specifically to an improved electrophoretic imaging system.

The system improved by this invention is of the type using photosensitive radiant energy absorbing particles believed to bear a charge when suspended in a nonconductive liquid carrier. The suspension of these par ticles in the carrier is placed in an electroded system to be exposed to an image radiation configuration. For a detailed description of the operation of this system see U.S. Pat. Nos. 3,384,565 issued May 21, 1968 in the names of V. Tulagin and L. M. Carreira, 3,384,566 to H. E. Clark and 3,383,993 issued on the same date to S. Yeh. The particles employed in this system migrate in image configuration providing a visual image at one or both of the electrodes between which they are placed. The system employs particles which are photosensitive and which apparently undergo a net charge alteration upon exposure to activating radiation by interaction with one of the electrodes. Various mixtures of two or more different colored particles can be used to secure the various colors of images and imaging mixes having different spectral responses. These colors can be used independently or even in subtractive color synthesis. In a monochromatic system the particles will migrate if energy of any wavelength within the panchromatic spectrum of the particle response strikes the particle.

It has been found that images produced by the system broadly described above may on occasion exhibit uneven density or contrast. Further, the apparatus employed for imaging is sometimes damaged during imaging. It is thought that these difficulties are caused by varying corona discharge or air ionization between the electrodes used for imaging as one electrode approaches the particle suspension in proximity to the other electrode. The invention herein was developed to eliminate this corona arcing between electrodes in an imaging system using a broad contact zone between electrodes during imaging within an electric field.

I Other inventions have been discovered for eliminating corona arcing between electrodes in an electrophoretic imaging system by taking a different approach or by using different apparatus from that of this invention. One such process is disclosed in copending application Ser. No. 519,034 filed on Jan. 6, 1968 in the name of L. M. Carreira now Pat. No. 3,485,738 issued Dec. 23, 1969 that discloses the use of a liquid placed between the blocking and injecting electrodes of an electrophoretic imaging system prior to the application of the field for actually forming the image.

Other approaches have been taken to eliminate corona arcing or air ionization between adjacent electrodes during imaging such as those in copending applications Ser. No. 821,202 now U.S. Pat. No. 3,697,407 issued Oct. 10, 1972 and Ser. No. 821,257 now U.S. Pat. No. 3,657,103 issued Apr. 18, 1972, filed concur- 2 rently with this application in the names of J. M. Lacagnina and R. G. Davies and D. J. Fisher and R. G. Davies respectively. In the first of the cited applications a member is positioned at the entrance and/or exit to the nip formed between the adjacent electrodes during imaging so that any air ionization occurs between one electrode and the member rather than between two electrodes. The manner in which the device actually functions generally eliminates corona arcing entirely. The second cited application utilizes a blocking electrode formed with an electrical backing member commutated behind the blocking surface. The electrical commutation of the blocking electrode is such that there is insufficient field at the entrance and exit of the nip formed between the two electrodes to cause corona arcing thereat.

Other apparatus that appears at: first to be similar to the apparatus shown in the instant application is disclosed in-copending application Ser. No. 452,651 filed May 3, 1965 now Pat. No. 3,474,019 in the name of Arthur L. Krieger et a1. and entitled lmaging Apparatus. However, the structure shown there is quite different from that of the instant application in that there is no provision for limiting the electric field within the contact zone of the electrode shown. The electric field is deliberately maintained over the entire contact zone and of necessity extends beyond this zone due to the electrical connections shown therein. The application here modifies that structure in that it limits the electrical connection preventing air ionization and corona arcing neither of which are eliminated by the above cited application.

Therefore, it is an object of this invention to improve electrophoretic imaging systems by eliminating corona arcing between electrodes. Another object of this invention is to improve systems using broad contact zones between relatively moving electrodes. Still another object is to allow use of reuseable or nonreuseable blocking surfaces in broad imaging contact.

The foregoing objects and others are accomplished in accordance with this invention by introducing an electric field at a blocking electrode surface between the blocking electrode and electrophoretic suspension held in proximity to another electrode such that the field is maintained within a contact zone established by the contact area of the two electrodes the field being limited in area to prevent a strong field at the extremes of the contact zones thereby eliminating air ionization and corona arcing thereat.

It may be that other systems exist or will be discovered or invented that require improvements similar to those described herein and this invention can be used thereon to improve such a system and such use in contemplated hereby.

The advantages of this improved electrophoretic imaging system will become further apparent upon consideration of the following detailed disclosure of the invention; especially when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic illustration of an imaging device employing this invention;

FIG. 2 is a schematic illustration of another embodiment of the invention; and

FIG. 3 is another schematic illustration of an embodiment of this invention.

Referring to the drawings there is shown in FIG. l a photoelectrophoretic imaging system having an injecting electrode, generally referred to by reference numeral 10, having a transparent glass substrate 12 and an electrically conductive layer 14. Both the glass and the overcoated layer are optically transparent. The structure may be of tin oxide coated on glass which is commercially available under the name NESA glass from Pittsburgh Plate Glass Co. Any other suitable structure usable within the imaging system is suitable for this invention. Deposited on the injecting electrode is a thin layer 16 of finely divided photosensitive particles dispersed in an insulating liquid carrier. This is the imaging suspension from which a final image is formed.

Adjacent to the electrode 10 and the suspension 16 thereon is a blocking electrode, generally referred to by the reference numeral 18, which has a blocking layer 20 formed around a plurality of roller guides 22, 24 and 26. These guides and the blocking material layer 20 surrounding them extend the entire width of the electrode l0 and form a tractor type moving device when the rollers are driven by a suitable drive mechanism, for example, motor M-l. This movement causes portions of the blocking layer 20 to lay down and then be picked up across the surface of the injecting electrode 10. Drive connections for the blocking electrode assembly are of the usual type and would be known to those skilled in the art of making such assemblies.

The term photosensitive for the purpose of this invention refers to the properties of a particle which, once attracted to the injecting electrode, will reverse its polarity and migrate away from it under the influence of an applied electric field when exposed to activating electromagnetic radiation. The term injecting electrode" for the purpose of this invention refers to the electrode the properties of which apparently inject charges into the photosensitive materials activated by electromagnetic radiation under the influence of an electric field. The term blocking electrode for the purpose of this invention refers to the property of an electrode which once contacted by activating photosensitive particles will not inject charge into a sufficient number of them to cause them to migrate from the blocking electrode surface. The term suspension may be defined as a system having solid particles dispersed in a solid, liquid or gas. Nevertheless, the suspensions described for illustrations herein are of the general type having a solid dispersed in a liquid carrier. For a more detailed, theoretical explanation of the apparent mechanisms of operation of this imaging pro cess, see the above mentioned patents, the disclosures of which are incorporated herein by reference.

The blocking electrode assembly has three rollers shown for support and guidance. The outer rollers 22 and 26 are formed of any material though preferably hard and relatively inflexible. Although their electrical characteristics are not critical, it may be desirable to have the outer rollers 22 and 26 formed of conductive material and maintain these rollers at the same electrical level as the conductive surface 14 of the injecting electrode 10. This helps prevent charge build-up on the surface 20 of the blocking electrode. The center roller 24 must contain a conductive core or be made ofa conductive material and should contact the lower surface of the blocking material 20 which is ofa high dielectric type material such as Tedlar, a polyvinyl fluoride commercially available from E. I. DuPont de Nemours Co., Inc. The roller 24 is electrically connected to a potential source 28 through a switch 30. An electric field is produced between the injecting electrode 10 and the conducting roller 24 when the switch 30 is closed. Between the two is the blocking surface 20 and the suspension 16.

The electric field is applied in proximity to the roller 24 as the blocking electrode assembly 18 moves across the suspension 16 on the surface of the injecting electrode 10 in the vicinity of the charged roller 24. The movement is in the direction shown by the arrow. The image to be made is formed by a projection system made up of a light source 32, a transparency 34 and a lens 36 positioned to project an image of the transparency at the suspension 16 on the injecting electrode 10.

FIG. 2 schematically shows a representation of this invention in a photoelectrophoretic imaging system wherein the improved blocking electrode is in the form of a disposable web 58. The injecting electrode shown herein generally referred to as electrode 10 is formed as a continuous plate shaped as a cylinder. Around the periphery of the electrode surface 40 are the various stations required to form a photoelectrophoretic image. They include a suspension dispensing system generally referred to as 42 and having a container 44 for holding the suspension 16 used for imaging. A conduit 46 brings the suspension to an applicator bar 48 which applies a more or less uniform, thin layer of the suspension 16 on the injecting electrode surface 40.

An optical system is provided to expose the suspension to activating electromagnetic radiation in the vicinity of the blocking electrode 18. The optical system has an electromagnetic radiation source 50 and a transparency 52 which is to be imaged at the interface of the blocking electrode 18 and the injecting electrode 40 through the lens 54 and past mirrors 55 and 56. Any suitable optical system for forming an image in the contact zone 57, being the broad area of contact at the interface of the two electrodes, is suitable for the application shown here.

The blocking electrode 18 is formed as a web 58 of a high dielectric material having a resistivitiy greater than 10 ohm-cm held on a supply spool 60 to be fed around guide rollers 62 and 64 to a take-up spool 66. Intermediate the guide rollers 62 and 64 which maintain the web 58 adjacent to the cylindrical injecting electrode surface 40 is an electric field generating device. The device shown here is a corona discharge device in the form of a corotron 68 which is electrically connected to a suitable source (not shown) to generate the proper field in close proximity to the corotron 68 between the blocking electrode web 58 and the injecting electrode surface 40 through the suspension 16 maintained therebetween. The corotron or any similar device may generate ac or dc corona to control the potential field at the blocking electrode.

The guide rollers 62 and 64 are preferably conductive and are held at the same potential as is the injecting electrode 40. By maintaining both the rollers 62 and 64 at the same potential as the injecting electrode a corona arc bridging the gap between the web 58 and the surface 40 of the injecting electrode 10 is eliminated. Typical voltages employed in this system for imaging while exposing may be in the range of 300-5,000 volts between the electrode surfaces in close proximity to the corotron 68. Since the web 58 is of a high dielectric material and generally non-conductive having a resistivity of l0 ohm-cm or greater, the electrical charge on the web 58 in proximity to the corotron 68 does not spread to the outer edges of the contact zone 57 between the web and the surface 40 of the injecting electrode 10. The corotron may be shielded to prevent any electric arcing between it and the rollers 62 and 64 even if the voltages and distances are such that arcing may otherwise tend to voccur.

Imaging of the photoelectrophoretic suspension takes place in the area between the web 58 and surface 40 where there is a sufficient electrical field to image under proper exposure conditions. This is the contact zone. lts maximum coverage as shown is delineated by the spacing numbered 57. The field as described, is narrowly maintained within the interface of the web 58 and the surface 40 so that it does not extend to the positions where the electrodes separate beyond the spacing referred to as 57. The take-up spool 66 is driven by suitable means to insure the proper velocity of the web 58 so that it moves in the direction shown in rolling contact with the surface 40 of the injecting electrode ll).

The image to be formed into the final copy is desig nated by numeral 72 and is carried by the cylindrical injecting electrode to contact an adhesive web 74 which is pressed against the injecting electrode surface by rollers 76 and 78 also functioning to guide the adhesive web 74;. ln this manner, the image 72 is transferred to the adhesive web 74 which maintains it thereon. The transferred image then may be fixed in place by lamination or, as shown by the figure, through a suitable fixing chamber 80 which may supply heat or some other means that will insure fixing of the image.

FIG. 3 shows another embodiment representing a modificiation of the embodiment of FIG. 2 which uses a disposable web 82 as the surface of the blocking electrode 18. The web is made to traverse the injecting electrode l0 formed as a flat plate. Although this embodiment does not give the benefit of continuous imaging as shown in FIG. 2, it does illustrate the use ofa disposable blocking electrode surface. The operation of the apparatus in this figure is similar to FIG. 2 in that the high dielectric blocking surface 82 moves in rolling contact with the suspension 16 on the conductive surface l tl of the injecting electrode 10.

The guide rollers 84 and 86 maintaining contact be tween the electrode surfaces in moving contact zone may be conductive although this is not absolutely required. Nevertheless. they are preferably maintained at the same potential as the conductive surface 14 of the injecting electrode in order to insure that there be no corona arcing between the two surfaces. The commutator bar 88 is electrically connected to a high voltage source to provide approximately between 3005,000 volts relative to the injecting electrode 10. it also insures close pressure contact in the high field contact zone. Exposure is achieved in the manner discussed in FIG. 1. The commutator bar 88 is positioned to maintain the electrical field in a limited area within the contact zone of the blocking surface 82 and the conductive surface 14 of the injecting electrode 10. The positioning in such that there is insufficient field at the edges between the electrodes to permit air ioniza tion or corona arcing.

While this invention has been described with reference to the structures disclosed herein and while certain theories have been expressed to explain the experimentally obtainable results, it is not confined to the details set forth; and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.

What is claimed is:

1. A method for eliminating electrical arcing during imaging of an photoelectrophoretic imaging suspension in an apparatus comprising a first transparent conductive electrode for supporting a layer of an imaging suspension; a flexible electrically insulating'web formed of a material having a resistivity greater than about 10 ohm-cm; contacting support means for contacting said web and the imaging suspension; separation support means for guiding said web away from the imaging suspension, said support means being positioned to cause said web to remain in contact with the layer of imaging suspension from said contacting support means to said separation support means; a second electrode for applying an electrical field across said web and the imag ing suspension in a contact zone; exposure means for exposing the imaging suspension to an image through said first transparent conductive electrode; and means for coupling said first and second electrodes to an electrical potential source, comprising the steps of: j

a. moving said web in rolling contact over said first transparent conductive electrode thereby causing said contact zone to move across said first transparent conductive electrode;

b. positioning said second electrode between said contacting and separation support means;

c. maintaining said contacting and said separation support means at approximately the same potential and polarity as said first transparent conductive electrode; and

d. applying an electrical field limitedly across said web and the imaging suspension in said contact zone between said contacting and separation support means such that electrical arcing at the line of contact and separation of said web and the imaging suspension is eliminated.

2. The method of claim ll wherein said flexible electrically insulating web has an endless surface and further including cleaning means for cleaning the surface of the web which contacts the imaging suspension.

=l= =l= k 

1. A METHOD FOR ELIMINATING ELECTRICAL ARCING DURING IMAGING OF AN PHOTOELECTROPHORETIC IMAGING SUSPENSION IN AN APPARATUS COMPRISING A FIST TRANSPARENT CONDUCTIVE ELECTRODE FOR SUPPORTING A LAYER OF AN IMAGING SUSPENSION; A FLEXIBLE ELECTRICALLY INSULATING WEB FORMED OF A MATERIAL HAVING A RESISTIVITY GREATER THAN ABOUT 10**7 OHM-CM; CONTACTING SUPPORT MEANS FOR CONTACTING SAID WEB AND THE IMAGING SUSPENSION; SEPARATION SUPPORT MEANS FOR GUIDING SAID WEB AWAY FROM THE IMAGING SUSPENSION, SAID SUPPORT MEANS BEING POSITIONED TO CAUSE SAID WEB TO REMAIN IN CONTACT WITH THE LAYER OF IMAGING SUSPENSION FROM SAID CONTACTING SUPPORT MEANS TO SAID SEPARATION SUPPORT MEANS; A SECOND ELECTRODE FOR APPLYING AN ELECTRICAL FIELD ACROSS SAID WEB AND THE IMAGING SUSPENSION IN A CONTACT ZONE; EXPOSURE MEANS FOR EXPOSING THE IMAGING SUSPENSION TO AN IMAGING THROUGH SAID FIRST TRANSPARENT CONDUCTIVE ELECTRODE; AND MEANS FOR COUPLING SAID FIRST AND SECOND ELECTRODES TO AN ELECTRICAL POTENTIAL SOURCE, COMPRISING THE STEPS OF: A. MOVING SAID WEB IN ROLLING CONTACT OVER SAID FIRST TRANSPARENT CONDUCTIVE LECTRODE THEREBY CAUSING SAID CONTACT ZONE TO MOVE ACROSS SAID FIRST TRANSPARENT CONDUCTIVE ELECTRODE; B. POSITIONING SAID SECOND ELECTRODE BETWEEN SAID CONTACTING SAID SEPARATION SUPPORT MEANS; C. MAINTAINING SAID CONTACTING AND SAID SEPARATION SUPPORT MEANS AT APPROXIMATELY THE SAME POTENTIAL AND POLARITY AS SAID FIRST TRANSPARENT CONDUCTIVE ELECTRODE; AND D. APPYING AN ELECTRICAL FIELD LIMITEDLY ACROSS SAID WEB AND THE IMAGING SUSPENSION IN SAID CONTACT ZONE BETWEEN SAID CONTACTING AND SEPARATION SUPPORT MEANS SUCH THAT ELECTRICAL ARCING AT THE LINE OF CONTACT AND SEPARATION OF SAID WEB AND THE IMAGING SUSPENSION IS ELIMINATED.
 2. The method of claim 1 wherein said flexible electrically insulating web has an endless surface and further including cleaning means for cleaning the surface of the web which contacts the imaging suspension. 